The mucopolysaccharidoses (MPS) are a group of hereditary diseases characterized by defective metabolism of glycosaminoglycans (GAGs). The disorders are usually associated with severe dysfunction of the nervous system as well as of liver, spleen, heart, bone, and other tissues. Objective of this project is the study of mechanism of pathogenesis of these diseases with emphasis on brain involvement and mental retardation. We are using a comparative approach. For this purpose we study the changes, in GAGs, sphingolipids, and pertinent lysosomal enzymes in tissues of patients with various types of MPS and we make correlation in terms of clinical and ultrastructural findings. Our laboratory contributed significantly in understanding the chemical pathology and in particular the neurochemistry of MPS IH, MPS IS, MPS II, MPS III A and MPS III B. To complement the studies with human subjects, a drug (suramin) induced animal model of MPS has been developed and a canine model, (natural), of MPS I (Alpha-L-iduronidase deficiency), has been fully characterized. In an attempt to reverse the progressive deterioration caused by this incurable metabolic disorder, five dogs with MPS I were transplanted with marrow from normal or heterozygous littermates. Transplanted bone marrow provides the affected dogs with self-renewing source of cells that produce the enzyme needed to complete the metabolic process. One year after transplantation the results are very encouraging for this neurodegenerative metabolic disorder because we found marked corrective changes within the central nervous system of the dogs.